Generally, heads for molding articles made of plastic material are known wherein the individual liquid components to be mixed are separately injected directly into a mixing chamber typically associated with a discharge duct which communicates with an associated mold. The liquid substituents to be mixed are injected into the mixing chamber through lateral orifices which open directly into the discharge duct and are directed generally normal to the flow path therethrough.
It has been found that the kinetic energy possessed by the streams of the individual liquid substituents is not completely dissipated in the mixing chamber. Consequently, the streams tend to extend into and along the discharge duct. The phenomenon results in, among other deleterious aspects, a flow of material from the discharge duct which is not thoroughly mixed. The resulting molded parts are subsequently subject to imperfections.
One of the solutions proposed for achieving complete mixing of the substituents involved is lengthening of the discharge duct to insure a complete dissipation of the kinetic energy in the streams of fluid substituents prior to the pouring or injection of the mixture into a mold cavity.
However, it has been found that lengthening the discharge duct to solve the aforedescribed problem actually introduces additional problems. Lengthening the discharge duct in the manner described above requires lengthening of the associated purge pin assembly for clearing the discharge duct between pouring cycles. The longer purge pin has additional mass, and hence greater inertia, thus requiring more operating energy to effect the desired purging operation.